Braun tube



E. SCH WARTZ BRAUN TUBE Oct. 25, 1938.

Filed June 29, 1935 Patented Oct. 25, 1938 Erich Schwartz, Berlin-Zchlcnflorf, .Germany, as'

signor to the firmf Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application June 29, 1935, SeralNo. 29,136

In Germany June3, 1934 v 1 Claim. (01. 250,27.5)

This invention relates to Braun tubes, and particularly to the construction of the hot cathode in cathode ray tubes for television or oscillegraphic purposes, and to a method of producing are arranged as in a horseshoebathode, vvhereas, according to Fig. 2, they are crossed to reduce the effect of the field produced by the leads upon the cathode ray. In Fig. 3, the leads are dis- 5 such cathodes. posedparallel and closely side by side to elimi- 5 One object of the invention is to provide a hot mate disturbing fields as much as possible. The cathode Whose emitting surface has coinciding spherical portion I may be covered wholly or axes of symmetry and rotation. partly with the emitting substance Il). 7

A further object of the invention is to form In Figure 3 the emitting substance Il] is shown 10 the cathode and arrange it relative to an eleccovering only the upper portion of the sphere l. 10 trode, such as a Wehnelt cylinder, so as to pro- In Fig. 4, the spherical part I rests on a pin vide, as much as possible, for linear dependence or bar4 surrounded by' a tube 5 of insulating maof the anode current upon the potential of the terial. On the outside of the tube 5 a hea n Wehnelt cylinder. winding is arranged, preferably in bifilar turns,

Another object of the invention isto produce and traversed by the current, the spherical part 15 a cathode which produces a bundle of electrons l'being connected toa suitable potential by th that converges from the very beginning instead pin 4. of a considerably diverging one as produced by Here only that portion of sphere l which is the cathodes hitherto in use. superior to tube5 is covered by emitting mate- Still another object of the invention is a cathrial l0. 20 ode which can be produced in a particularly The hot cathodes are preferably produced acsimple manner and which has a favorable heatcording to the invention by twisting together ing power. the points of two wires or by bending one wire According to the invention, the cathode surto form a horseshoe cathode and melting the 5 face has the shape of a sphere or a sector thereof point of this cathode, for instance by a blower and the preferred method of producing a cathode flanie, until the tip thereof has the shape of a comprises the steps of first constructing a horsespherical drop. Melting is continued or intershoe type-cathode, then imparting to the point rupted in time'so as to impart the desired size thereof drop shape by melting and finally apply-. to the diameter of the spherical part. In the ing thereto the emitting substance. construction the hitherto employed cathode ma- 0 A cathode according to the invention has a terial, such as platinum or platinumnickel may relatively long life and aiords numerous othr be used. V advantages which will be pointed out below With A hot cathode made in the manner described reference to the accompanying drawing which, is distinguished by high filament power, since,*

by way of example, illustrates the invention and owing to the melting process the current sup- 35 in which plying wire and the emitting surface form a unit L Figures 1, 2 and 3 show, on an enlarged scale, whereby harmful heat transition resistances are a cathode according to the invention, and indiprevented. cate an emissive coating thereon; It Will be round-in operation that the cathode 40 Fig. 4 is a view of an indirectly heated cathode; constitutes an advantage0us construction with 40 Fig. 5, a view of a cathode and adjacent conrespect to heating and the course of the heating trol electrode; and current, because the current fibws chiefiy through Figs. 6, 7a and 7b show cathodes of the hitherthe lower part of the sphere, so that, owing to the to usual type in comparison With which the merdistance of the emitting surface from the part its of the new construction are indicated. traversed by the current, the group of electronic 45 Referring to the drawing, the cathodes shown rays is not disturbed by the magnetic field of in Figs. 1, 2 and 3 have each a spherical part I the heating wire.

provided With an emitting substance I!) and two A further advantage during operation of the leads 2 and 3 connected to the spherical part I cathode is that a converging pencil of rays havand serving also as carriers and current supplies ing coinciding axes of symmetry and rotation is 50 for the latter. formed. Fig. 5 shows part of a Wehnelt cylinder The emitting substance Il] is shown as cover- 1 and the course of the potential if the Wehnelt ing the entire sphere 1, except the junctures With cylinder is negative relative tothe cathode. The legs 2 and 3, in Figures 1 and 2. potential surface 0 always starts vertically to r In the construction shown in Fig. 1 the leads 55 the cathode surface. The effective emitting part of the cathode is the calotte located on the positive side of the potential surface 0. The indicated course of the potential shows that the pencil of rays designated by broken lines and coming from the cathode is convergent.

Figs. 6, 701 and '71) illustrate cathode types of the usual kind to bring out the difierence between the art and the invention. At the pointof the cathode 8 in Fig. 6 the potential surface forms so that the extreme end of the cathode emits and a considerably diverging group of rays is produced, so that it is necessary to shield considerable portions of the cathode ray whereb the current yield of the tube isreduced. The horseshoe cathode 9, of whichFigs. 7a and 7b are,

respectively, front and side views, generates in one direction, 1. e., in the plane of Fig. 7b;;a

distribution of intensity in the electronic 'ray i thereore correspondingly -unsymmetrical, s0

that frequently two separate electronic rays are formed. The spherical cathode according to the invention, on the other hand, affords as stated the advantage of insuring the production of a convergent pencil of rays, in which the axes of symmetry and rotation concide.

I claim:

A Bran tube Cathode comprising a spherical portion, an electron emissive coating covering a substantial part of said spherical portion, supporting means formed integrally therewith extending from the nonemissive part thereof, an

'insulating supporting member surrounding and contacting said supporting means and engaging the noneini ssive part of said spherical portion in direct heat transferfing relationshp thereto, and means disposed about said insulating member for;heating said insulating member and causing a conductive heat transfer to said supporting means and said spherical portion.

x ERICH SCHWARTZ. 

